The present invention relates to an objective lens actuator, for fitting a focus position of an objective lens upon an target track on a recording surface of an optical disc, with driving the objective lens into a focusing direction and a tracking direction, so as to conduct reproducing or recording of information, which is recorded on the recording surface of the optical disc, and also a disc apparatus applying the same therein.
With the disc apparatus for recording information onto a disc-like information recording medium, or for reproducing the information recording thereon, an improvement of data transfer rate is achieved by rotating the optical disc with high speed. In the disc apparatus is mounted an objective lens actuator for driving the objective lens into the focusing direction and the tracking direction, so as to record and reproduce the information, correctly, with following a track on the optical disc.
In general, such objective lens actuator is constructed with a magnetic circuit, including a yoke and a permanent magnet, a moving portion including an objective lens and a driving coil attached therewith, a stationary or fixed portion for holding this moving portion thereon, and supporting members for elastically supporting the moving portion, which is connected with the fixed portion. When current flows through a focusing coil, within the magnetic field produced by the magnetic circuit including the yoke and the permanent magnet, then an electro-magnetic force is generated, and thereby the moving portion is driven into the focusing direction. In the similar manner, when current flows through a tracking coil, within the magnetic field produced by the magnetic circuit including the yoke and the permanent magnet, then an electro-magnetic force is generated, and thereby the moving portion is driven into the tracking direction.
For such the objective lens actuator, the following three (3) characteristics are required, mainly. First of all, for achieving a high accuracy positioning control while suppressing deflections due to disturbances, such as, wobbling and/or eccentricity of the disc, etc., it is necessary to increase driving sensitivity to be high. Next, for increasing control band fitting to high-speed of rotation number of the optical disc, it is necessary to bring amplitude to be small, at high-order resonance frequency of an elastic deformation mode of the moving portion. And, for dealing with high density while suppressing an aberration, which will be a cause of signal deterioration, it is necessary to reduce the tilt of the objective lens.
Among of those, in particular, relating to the driving sensitivity, there is already known an objective lens actuator, wherein a magnet is constructed with a first wide-width magnetic pole located at a center along the tracking direction, and second magnetic poles on both sides thereof, putting the first magnetic pole between them, and two (2) sides of the tracking coils provided in plural numbers thereof, on an inner side and an outer side thereof, are attached, opposing to the first magnetic pole and the second magnetic pole, respectively, thereby winding one (1) piece of the focusing coil around a peripheral side surface of the moving portion, and also a boundary portion between the magnetic poles of the magnet is disposed outside than the both side edges of the yoke (an example shown in the following Patent Document 1). With this, in the focusing direction, it is possible to increase a number of magnetic fluxes crossing the focusing coil, and also in the tracking direction, it is possible to generate driving forces on both sides, i.e., an inner side and an outer side of each tracking coil; thereby achieving an improvement of the driving sensitivity.
[Patent Document 1] Japanese Patent Laying-Open No. 2005-38496 (2005) (Claim 1 and FIG. 2).